Apparatus for loading transmission circuits



Jan. 11, 1927. 1,613,958

E. B. PAYNE APPARATUS FOR LOADING TRANSMISSION CIRCUITS:

Filed Dec. 18, 1923 f/y/j Patented Jan. 1 1 1927.

UNITED Y STATES PATENT oFFlcE.

EDWARD B. PAYNE, OF GREAT NECK, NEW YORK, ASSIGNOR TO WESTERN ELECTRIC COMPANY, INCORPORATED, 015 NEW YORK, N. Y., A CORPORATION OF NEW YORK.

APPARATUS FOR LOADING TRANSMISSION CIRCUITS.

Application filed December 18, 1923. Serial No. 681,337.

This .invention relates to apparatus for loading transmission circuits and has for its object the reduction of cross talk in the circuits.

As is well known in the art, it is desirable,

in long distance telephone systems to combine the four line conductors of two physical circuits to form a third or phantom circuit, the two conductors of one physical circuit,

in parallel, forming one side of the phantom circuit andthe two conductors of the other physical circuit, in parallel, forming the other side of the phantom circuit. The four, conductors when used to make up such a set ll of three circuits are known as a quad. One way of loading such a transmission circuit is to provide three loading coils, two of which provide loading for the two physical, or side circuits, and the third, for the phantom cir- W cuit. The method of constructing and connecting such loading coils is well known.

'It is often found desirable to mount in a common casing loading coils for a plurality of lines. Especially is this true when the lines go together to make up a cable. When loading coils are mounted in this manner it is the general practice to mount the side circuit coils and the phantom circuit coils on separate spindles. This practice makes necessary the use of connecting quads within the casing which not only requires considerable space but also greatly'increases the difficulty of assembling. When the coils are assembled in this manner it is impossible, in certain cases, to reduce the objectionable side to side cross talk to a satisfactory minimum.

The mutual inductance between sectionalized coils of the toroidal type, such as are used for telephone line loading, can be varied by varying the relative angular position of the coils. By this method, it is possible to reduce to a minimum, cross talk between the side circuitloading coils. Phantom circuit loading coils are constructed in such a man ner as to introduce inductance into the phantom circuit while not affecting the associated side'circuits. This is acomplishecl by mount ing on a common core foursectionalized w1nclings. Two of these windings are connected to each pair of line conductors, the inductances of the two windings connected to each pair neutralizing each other for currents together on a common spindle, the two side circuit coils being placed on the same side 'of the phantom circuit coil. When the loading coils are assembled in this manner, the inductive cross talk between the side circuit coils can be used to counterbalance the sideto side cross talk, particularly the inductive cross talk, introduced by the phantom circuit coil as hereinafter explained in detail.

This invention will be more fully understood by reference to the following description, in connection with the drawing in which: Fig. 1 shows a sectional view of a loading coil casing embodying this invention; Fig. '2 is a diagram of the connections of the loading coils; and Fig. 3, a detail of the angular relationship of the coils.

Referring to Fig. 1, the outer shell 35 which is preferably made of cast iron, is shown. Within the shell are placed a number of spindles 4 made of some non-magnetic material. Before the spindles are mounted in the case the loading coils 6, 7 and 8 are assembled on them. These loading coils are of the usual type in which the coils are wound in sections on separate portions of the toroidal cores, the sections being separated from oneanother by insulating washers. The loading coils are assembled in unit formation, the phantom loading coil 8 being placed below the two side circuit coils 6 and 7. Separators 5, composed of iron washers with fibre washers stacked on both sides, are placed between the coils. The iron washers actas a magnetic shield between the coils and it may sometimes be desirable to increase the mutual inductanc-es by omitting them. This method of assembling the coils in unit formation with the two side circuit coils on the same side of the phantom coil not only makes possible the reduction of side to side cross talk within the unit circuit coils and 8 the circuitto side circuit as hereinafter explained in detail, but also greatly reduces the side circuit to side circuit cross talk between the units since the side circuit coils of each unit are separated from the side circuit coils of the adjacent unit by the phantom coil. After the coils are assembled the connections are made.

The method of making the connections can best be explained by reference to Figs. 1

- and 2. For the sake of clearness, the same of the core.

All connections are left slack in order to permit rotating the coils to recuce the side cross talk. In Fig. 1

in the left hand group of coils, that side on which the interconnecting wires are located is shown, while in the right hand group are shown the connections of the spindle cables 10 and 11. These cables are branched E from the main cable 12, the splices being made in the open space above the coils. The lines coming from one direction are included in cable 10, those from the other in cable 11. The lines 16 and 17 of cable are connected'to coil 6 while 18 and 19 are connected to coil 7. The intermediate quads comprising conductors 20, 21, 22 and 23 serve to connect the two side circuit coils to the phantom circuit coil as shown. The other side of the phantom circuit coil is connected through conductors Qt, 25, 26 and 27 of spindle cable 11 to the line goingin the opposite direction.

In describing the method of mounting and connecting the loading coils, only one group was referred to since the other groups are assembled in a similar manner.

Before the coils are finally clamped by tightening the nuts on the ends of the spindles,'their angular positions are adjusted to give the minimum cross-talk. The meth- 7 0d of making this adjustment can best be understood by reference to Fig. 3 which is an enlarged view looking in the direction 3-3 in Fig. 1. In this view are shown the loading coils with the spindle cables 10 and 11 intheir approximate location. The winding separators of the phantom circuit coil 8 are shown by the dotted lines 30; those of the lower side circuit coil 7 by the dotted lines 31and those of the upper side circuit coil (Sby the dotted lines 32. The lower side circuit coil is rotated until its separators 31 make, with the separators 30 of the v phantom circuit proximately 22 jcoil is then rotated until the side-toside coil, the angle A ap- The upper side circuit cross-talk within the unit is a minimum.

If there is no unbalance due to imperfections in the coils, minimum cross-talk will be obtained when the separators of the side circuit coils are at the angle B, approximately since atthat angle the mutual inductance between the two side circuit coils is a minimum. Usually there is some I side-toside cross-talk introduced by unbalance in the phantom circuit coils. This can be counterbalanced by adjusting the mutual inductance between the side circuit coils by rotating the upper side circuit coil as explained above. In order notto disturb the connections, the coil 6 should only be rotated within the angle XOY. V

At times, there will be an unbalance of mutual inductance between the lower side circuit coil and the phantom circuit coil which will cause side-to-side cross-talk. Under these circumstances, it may be necessary to raise the upper side circuit coil to such a position that there will be no material mutual inductance between the side circuit coils, then to rotate the lower side circuit coil until the cross-talk reaches a minimum, and lastly to adjust the position of the upper side circuit coil as in the first case.

hat is claimed is:

1. A loading unit comprising a phantom circuit loading coil, a plurality of side circuit loadingcoils, all of said coils having separate magnetic circuits and means for adjustably mounting said side circuit coils together on the same side of said phantom circuit coil concentric with each other and with said phantom circuit. coil, to reduce the cross-talk.

2. A loading unit comprising a phantom circuit loading coil, a side circuit loading coil, a second side circuit loading coil, and means for concentrically mounting said loading coils whereby said loading coils may be rotated relative to one another to reduce the cross-talk, said first mentioned side circuit loading coil being mounted adjacent to said phantom circuit loading coil and said second mentioned side circuit loading coil being mounted adjacent to said first mentioned side circuit loading coil. 1

3. A loading unit comprising a phantom circuit loading coil, aside circuit loading coil, a second side circuit loading coil, and means for concentrically mounting said side circuit loading coils together. on the same side of said phantom circuit loading coil whereby said loading coils may be rotated relative to one another for adjusting the side circuit to side circuit cross-talk.

4. A loading unit comprisinga spindle, a phantom circuit loading coil mounted thereon, a side circuit loading coil mounted on said spindle and placed adjacent to said phantom circuit loading coil, and a second side circuit loading coil mounted on said spindle and placed adjacent to said first mentioned side circuit loadin r coil, said coils being adjustably mounte to control the cross-talk.

5. A loading coil case comprising an outer housing, a plurality of spindles mounted therein, and .a plurality of loading units mounted on said spindles, each of said units comprising a phantom circuit loading coil, a

side circuit loading coil mounted adjacent to cuit loading coil and rotating said coils relative to one another until the side circuit to side circuit cross-talk is a minimum.

7. The method of adjusting the side circuit to side circuit cross-talk in a transmission system loaded by means of a phantom circuit loading coil and a plurality of side circuit loading coils, which comprises placing one of said side circuit loading coils adjacent to said phantom circuit loading coil, rotating said first side circuit loading coil until it makes a given angle With said phantom circuit loading coil, placing a second side circuit loading coil adjacent to said first mentioned side circuit loading coil, and rotating said second side circuit loading coil until the side circuit to side circuit crosstalk is a minimum.

In Witness whereof, I hereunto subscribe my name this 14 day of December A. D., 1923.

EDWARD B. PAYNE. 

